Torque motor actuators are used in myriad systems and environments. For example, many valves associated with an aircraft gas turbine engine are controlled using torque motor actuators. No matter the specific end-use system and environment, a typical torque motor actuator includes a plurality of magnets, a plurality of magnetic pole pieces, a plurality of coils, an armature, and a lever. The coils are controllably energized to generate a magnetic force that is transmitted through the pole pieces and across air gaps into which portions of the armature extend. The magnetic force acts on and controls the rotational position of the armature. By controlling the rotational position of the armature, the position of a lever, a valve element, or other device, is controlled.
In many instances, the air gaps between the magnetic pole pieces and the armature are of a distance that is greater than the structural capability of the armature support geometry. Additionally, if the armature gets too close to a pole piece, the armature may undesirably latch to the pole piece. For these reasons, along with calibration considerations, the armature rotational displacement is limited.
Presently, armature rotational displacement is limited by incorporating non-magnetic stops into one or both sides of one of the magnetic pole pieces, usually the upper pole piece. Typically, two stops are used to limit the rotational displacement in each direction. These stops are typically implemented using threaded stop screws that are threaded into the pole piece, and onto which jam nuts are threaded. Typically, after the stop distance is set, a wicking anaerobic sealant is applied to the threaded stops and jam nuts to prevent any unintended movement thereof.
Presently known armature stops are generally effective, but do exhibit certain drawbacks. For example, these known stops may exhibit relatively high manufacturing, procurement, and calibration cost. In particular, the stop screws need to be of a small diameter to limit the amount of magnetic material removed from the pole piece, and have a relatively high length-to-diameter ratio, creating manufacturing challenges for the screw and the threaded hole in the pole piece. In addition to the long thread length, the magnetic material of the pole piece can be difficult to tap. Moreover, the adjustment and locking of the stop screws, via the lock nuts and wicking anaerobic sealant, can be difficult and costly.
Hence, there is a need for a torque motor actuator that includes an armature stop that is not costly to manufacture and/or calibrate. The present invention addresses at least this need.